1. Field of the Invention
The present invention relates to food colouring substances useful, for example in the manufacture of food products, sweets and pharmaceutical products.
2. Background
Colouring substances containing natural or synthetic colouring substances are commonly used in the manufacturing of food products and pharmaceutical products. A wide range of synthetic colouring substances are commercially available making it possible for the manufacturer of food products, sweets and pharmaceutical products, where a particular colour tone is desired, to select a single colouring substance having the desired colour or a mixture of colouring substances, which in appropriate combination impart the desired colour to the product.
Due to consumer pressure there is a trend to replace the synthetic colouring substances with natural ones. However, the use of natural colouring substances implies various problems such as lack of blue colour, acceptable in food substances, unpleasant taste and odour and bleeding, (i.e. diffusion of colour from the food into the environment). These three problems will in the following be presented in more detail and a coherent solution will be disclosed.
Firstly, one problem is that most natural colouring substances used in food products are red, orange or yellow and not blue. There are presently no natural blue colouring substances that are legally approvable for use in foodstuffs marketed in Europe and the USA.
The same problem applies to some extent to green colours. Copper chlorophyll and copper chlorophyllin are efficient and relatively stable green colouring substances but in some countries they are not considered “natural” from a legislation point of view. If a satisfactory natural blue colouring substance could be produced, one might produce a natural green by blending it with a natural yellow colour substance like e.g. turmeric.
It is known from the prior art that some anthocyanins, for example those found in red cabbage leaves, give a blue colour in alkaline solution. Thus, a bright blue colour is normally obtainable at high pHs (almost 8 and above) which is inappropriate for food usage, e.g. Grube, O. et al. “The pigment of red cabbage as an indicator in the pH range 8.5-10.”, Chem. Ztg., 67, 34, 1943. However, in this range of pH anthocyanins and other food ingredients are often unstable.
The existence and preparation of blue complexes with aluminium and magnesium from anthocyanins derived from petals and sepals from the flowers of hydrangea and Chinese bellflower is known from the prior art.
Chenery revealed in “The problem of the blue hydrangea” J. Roy. Hort. Soc., 62, 304 (1937) noted that hydrangea hortensis petals would turn blue if its soil was watered with aluminium salts and that aluminium would accumulate in the petals. No such effect on anthocyanins present in or derived from other parts of plants such as e.g. red cabbage leaves or purple carrots was mentioned.
Susumu Maekawa et al. found in “Effect of Aluminium Ions on the bluing of Petal Color in Cut Chinese Bellflower, Platycodon grandiflorum”, Plant & Cell Physiol. 24(4): 759-764 (1983) that petal colour of Chinese bellflower changed from blue-violet to blue after cut flowers were placed in a solution containing aluminium ions. This was also observed when aluminium ions were added to a solution of anthocyanins extracted from petals from this flower. No such effect on anthocyanins present in or derived from other parts of plants such as e.g. red cabbage leaves or purple carrots was mentioned.
Asen and Siegelman: “Effect of Aluminium on Absorption Spectra of the Anthocyanin and Flavonols from Sepals of Hydrangea macrophylla var. Merveille”, Proc. Am. Soc. Hort. Sci. 70, 478 (1957) found that addition of aluminium to a solution of anthocyanins extracted from Hydrangea macrophylla var. Merveille could change the colour of the solution from red to blue. No such effect on anthocyanins present in or derived from other parts of plants such as e.g. red cabbage leaves or purple carrots was mentioned.
Kosaku Takeda et al.: “Blueing of sepal colour of Hydrangea macrophylla”, Petrochemistry, vol. 24, No. 10, pp. 2251-2254, 1985 found that the blue colour of Hydrangea macrophylla sepals was mainly due to a blue anthocyanin-aluminium complex.
No reference was made to anthocyanins present in or derived from other parts of plants such as e.g. red cabbage leaves or purple carrots.
EP 0 873 680 A1 describes a method of changing the colours of petals containing anthocyanin in a more bluish direction by the addition of a Lewis acid or aluminium salts, but without mentioning any such effect on anthocyanins present in or derived from other parts of plants such as e.g. red cabbage leaves or purple carrots.
A major difference between the anthocyanins from these flowers and the ones from red cabbage is that the anthocyanins from the flowers mainly consist of delphinidin derivatives and the anthocyanin from red cabbage mainly consists of cyanidin-3-glucosides. (Jurd and Asen (1966), and Takeda et al. (1990)
Jurd & Asen (1966) and Takeda (1990) have published a few in vitro studies on metal, including aluminium, complexes with purified anthocyanins, including cyanidin-3-glucoside.
Jurd and Asen (1966) added quercitrin and chlorogenic acid to solutions of purified cyanidin-3-glucoside and aluminium at pH 5.5. With quercitrin a cerise complex formed. With chlorogenic acid an insoluble, almost blue, extremely insoluble precipitate formed.
Takeda et al. (1990) added 3-p-coumaroylquinic acid to solutions of purified cyanidin-3-glucoside and aluminium at pH 3.7. Increasing levels of 3-p-coumaroylquinic acid gave a more bluish-purple colour hue.
Secondly, another problem by using natural colouring substances for obtaining a blue colour is that extracts containing anthocyanins, especially red cabbage extract, are typically associated with unpleasant tastes and odours when applied in food products, sweets and pharmaceutical products which is a disadvantage Prior art such as Sapers, G M., “Deodorization of a colorant prepared from red cabbage.”, J Food Sci., 47, pp. 972-976, 1982 discloses methods for solving this problem through purification steps However, these methods suffer from being insufficient as the unpleasant tastes and odours often develop after the purification of the anthocyanin has been performed In conclusion it has so far been technically impossible to permanently remove the organoleptical problems associated with extracts from vegetables such as red cabbage and purple carrot.
Thirdly, yet an additional problem by using natural colouring substances for obtaining a blue colour, is that as anthocyanins are more or less water soluble, they will leak and “bleed” if in an aqueous environment. This is particular a visible problem if used in a multi-compartment food system where the different compartments have different colours.
The above three problems associated with the use of natural colouring substances have been presented and it is obvious that the problems concentrate mainly on lack of availability of legal and technical requirements.
The preparation of aluminium lakes of dyes is well-described for a lot of dyes, especially synthetic dyes. However, no aluminium lakes of anthocyanins or blue lakes of other natural colouring substances have been described hitherto, that are legally acceptable in food substances.
U.S. Pat. No. 833,602 teaches a laking process involving acid colouring materials and alkaline aluminium salts. However, only lakes of synthetic colouring materials are described.
U.S. Pat. No. 2,053,208 teaches a Taking process for synthetic dyes using aluminium sulphate and sodium aluminate. However, sodium aluminate is not allowed as a process aid for manufacturing of colouring aids for foods according to food legislation in the EU.
W. A. Blumenthal gives in “American Dyestuff Reporter”, Nov. 18, 1946, vol. 23, pp 529-545 a review on colour lakes. He mostly deals with lakes of synthetic colours but he also briefly describes lakes of some natural dyes: cochineal, lac-dye, alkermes, Indian yellow, purple snail, logwood, fustet, quercitron, indigo, redwood. None of these lakes based upon natural dyes contain anthocyanins to any significant degree.
U.S. Pat. No. 3,909,284 describes a method of making dry edible non-toxic colour lakes approvable for food and drug use by reacting synthetic colouring substances with sodium hydrogen carbonate and aluminium chloride under very specific conditions. However, only laking with synthetic colouring substances is described.
EP 0 025 637 A1 teaches methods of producing different metal lakes of the natural colouring substance curcumin which is very different from anthocyanins.
U.S. Pat. No. 4,475,919 describes a method of providing lakes of natural colouring substances for foods with starch or cellulose. No aluminium lakes of anthocyanins are mentioned or obvious.
None of the above references disclose any solution or circumvention to firstly the desire of providing natural blue colouring substances that are legally approvable for use in foodstuffs and are blue at normal food pH values, and secondly the market need of providing a lasting removal of the organoleptical problems associated with extracts from vegetables such as e.g. red cabbage and purple carrot.